This invention is related to cementing a well that is drilled into the earth and more particularly relates to a method of forming a lightweight or low density slurry and using this lightweight slurry in the cementing of the well.
In the completion of a well drilled into the earth, pipe or casing is normally lowered into the well and a cement slurry is pumped down the well and up the annular space formed between the pipe and the wall of the well. The cement slurry is then maintained in the annular space and allowed to set and bond the pipe to the wall of the well to thereby hold the pipe in place and prevent fluids from flowing behind the pipe. Many different cements and cement slurries have been used for this purpose though portland cement and calcium aluminate cement are probably the most common. Various additives and formulations have been used with these cements in forming slurries having particularly desirable properties. For example, bentonite and attapulgite clays have been added to cement slurries as have sodium chloride, calcium chloride, dispersing agents and gypsum.
In U.S. Pat. No. 2,582,459 to Richard A. Satterfield, bentonite and a soluble salt of a sulfonic acid are added to portland cement to produce an oil well cement which has low mechanical strength and will not shatter upon impact. In U.S. Pat. No. 3,071,481 to Horace J. Beach et al, there is described a gel cement composition for use in cementing wells. This composition consists essentially of a hydraulic cement, a colloidal clay, sodium chloride or calcium chloride and an organic dispersing agent. In U.S. Pat. No. 3,197,317 to Freeman D. Patchen, attapulgite is added to portland cement slurries for use in oil well cementing to reduce the density of the slurries. In U.S. Pat. No. 3,227,213 to Dwight K. Smith, water swelling clays, such as bentonite or attapulgite, are prehydrated and then mixed with hydraulic cement of the character of portland to form a slurry having a much higher yield than a slurry utilizing dry bentonite. In U.S. Pat. No. 3,581,825 to Joseph U. Messenger, there is described a method of cementing wells wherein slurries of calcium aluminate cement and clay selected from the group of bentonite, attapulgite and mixtures thereof are used, which slurries are particularly applicable for use in cementing behind casing in permafrost zones.